Lithium polymer battery with external sheath

ABSTRACT

A lithium polymer battery comprising an internal sheath, reinforcement members, and an external sheath and a method for manufacturing the same are provided. The lithium polymer battery comprises a pouch-type internal sheath with an electrode assembly positioned therein and a protective circuit module that is attached to the surface thereof to control the charging and discharging processes of the electrode assembly. The battery further comprises reinforcement members that couple with surfaces of the internal sheath and an external sheath for integrally enclosing the internal sheath and the reinforcement members. The external sheath may comprise a tube, a thermally contractible tube, or a melted resin.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2004-0077224, filed on Sep. 24, 2004, which is herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lithium polymer battery and a methodfor manufacturing the same. In particular, the present invention relatesto a lithium polymer battery that is capable of forming a simpleexternal sheath while securing reinforcement members and a method formanufacturing the same.

2. Description of the Prior Art

As generally known in the art, a lithium polymer battery has a separatorthat is positioned in between a positive electrode plate and a negativeelectrode plate to serve as a medium for ion conductance and as a mediumfor separating the electrodes in the lithium ion battery. The separatormay comprise a gel-type polymer electrolyte, which is prepared byimpregnating a polymer with an electrolyte to improve ion conductivity.

In addition to improved ion conductivity, the gel-type polymerelectrolyte has the advantages of excellent bonding to electrodes,mechanical properties, and a simple manufacturing process. A PVDF-basedelectrolyte (available from Bellcore Company) is a gel-type polymerelectrolyte that is prepared by mixing a copolymer of vinylidenefluoride (VDF) and hexafluoroethylene (HFE), a plasticizer, and aninorganic additive to form a film, impregnating it with an electrolyte,and causing it to gel.

The characteristics of lithium polymer batteries and lithium ionbatteries will now be compared briefly.

Lithium polymer batteries may have a plate structure and do not need tobe wound as in the case of lithium ion batteries. Therefore, theelectrode assembly comprising a number of positive electrode, a negativeelectrode, and a separator plates can be laminated and may be suitablefor use in a rectangular structure. Of course, lithium polymer batteriescan have a wound electrode assembly.

In addition, the electrolyte in a lithium polymer battery is injectedinto a completely integrated electrode assembly which prevents leakageof the electrolyte.

The plate structure of an electrode assembly of a lithium polymerbattery does not require the application of pressure to form arectangular shape. Therefore, a thin flexible pouch may be used as thebattery sheath instead of a hard rectangular or cylindrical can.

When a flexible pouch is used as the sheath of a lithium polymerbattery, the thickness of the resulting battery is substantially reducedcompared with using a can as the sheath. In addition, more electrodeassemblies can be contained in the same volume. This increases the powerstorage capacity of the battery. The battery can be easily manufacturedin any desired shape due to the flexible sheath and can easily bemounted on a variety of external devices.

However, such a pouch-type lithium polymer battery has various problemsresulting from its weak protective cover. For example, if the pouch-typesheath of a conventional lithium polymer battery is pierced by a sharpobject such as a needle or a nail, a puncture is easily formed. If thesheath is bitten by a pet, it is easily torn off. Furthermore, when asharp object penetrates the sheath and contacts the internal electrodeassembly, the internal positive electrode plate and the negativeelectrode plate may be short-circuited. The battery may then catch fireor explode.

Conventional lithium polymer batteries do not radiate heat well and thismay shorten the lifespan of the battery. The pouch-type sheath basicallyhas an insulation layer that is formed on its surface which degradesradiation performance and cannot actively dissipate that is generatedwhen charging or discharging the battery. Furthermore, as thetemperature rises, the rate of discharge increases thus drasticallyshortening the lifespan of the battery.

When the temperature of the battery rises above a reference level due toover-heating, the electrode assembly or the electrolyte decomposes and alarge amount of gas is generated. This causes the sheath to swell easilysince it comprises a flexible material. The sheath also swells severelydue to heat that is supplied from the exterior.

Meanwhile, the battery sheath of conventional lithium polymer batteriesuse metal foil as the core layer. However, the metal foil is exposed tothe exterior along the edge of the battery sheath and is very likely tobe short-circuited to a conductor of a protective circuit module or anexternal set.

SUMMARY OF THE INVENTION

The present invention provides a lithium polymer battery that is capableof improving strength and suppressing swelling and a method formanufacturing the same.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

The present invention discloses a lithium polymer battery that comprisesa pouch-type internal sheath that has an electrode assembly that ispositioned therein and a protective circuit module that is attached tothe surface thereof to control the charging and discharging processes ofthe electrode assembly. The battery further comprises reinforcementmembers that are fastened to both surfaces of the internal sheath and anexternal sheath for integrally enclosing the internal sheath and thereinforcement members.

The present invention also discloses a method for manufacturing alithium polymer battery including the steps of providing an internalpouch-type sheath, placing an electrode assembly inside the internalsheath, and then sealing it. The method also includes coupling aprotective circuit module to the electrode assembly outside the internalsheath, fastening reinforcement members to both facing surfaces of theinternal sheath, and forming an external sheath to enclose the surfaceof the-reinforcement members and the internal sheath.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1A is a perspective view of a lithium polymer battery according toan embodiment of the present invention.

FIG. 1B is a partially exploded perspective view of the lithium polymerbattery of FIG. 1A.

FIG. 2A is a sectional view taken along line 2 a-2 a of FIG. 1A.

FIG. 2B is a sectional view taken along line 2 b-2 b of FIG. 1A.

FIG. 2C is a sectional view taken along line 2 c-2 c of FIG. 1A.

FIG. 3 is a flowchart illustrating a method for manufacturing a lithiumpolymer battery according to an embodiment of the present invention.

FIG. 4A, FIG. 4B, FIG. 4C, FIG. 4D, FIG. 4E, FIG. 4F, FIG. 4G, and FIG.4H are perspective views of manufacturing steps of the methodillustrated in FIG. 3.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The lithium polymer battery according to the present invention hasreinforcement members that are positioned on both surfaces of theinternal sheath which have a comparatively large area to improve overallstrength. This reduces the chance of the battery being penetrated by asharp object or tearing off the internal sheath. Swelling in the batteryis also suppressed. In addition, the manufacturing process for thebattery is simple and inexpensive.

The reinforcement members that are fastened to the internal sheath alsoimprove the heat radiation. Although the internal sheath has aninsulation layer that is formed on its surface it also has a poorthermal conductivity. The reinforcement members that are formed on thesurface of the internal sheath have excellent thermal conductivity.

The internal sheath is completely enclosed by the external sheath andthe metal film constituting the internal sheath is not being exposed tothe exterior. As a result, a short circuit between the metal film and anexternal object may be prevented.

FIG. 1A is a perspective view of a lithium polymer battery according toan exemplary embodiment of the present invention and FIG. 1B is apartially exploded perspective view of the lithium polymer battery shownin FIG. 1A. FIG. 2A is a sectional view taken along line 2 a-2 a of FIG.1A, FIG. 2B is a sectional view taken along line 2 b-2 b of FIG. 1A, andFIG. 2C is a sectional view taken along line 2 c-2 c of FIG. 1A. FIG.1A, FIG. 1B, FIG. 2A, FIG. 2B, and FIG. 2C will now be referred tosimultaneously.

As shown, a lithium polymer battery 100 according to the presentinvention generally comprises an internal sheath 110, reinforcementmembers 120 that are fastened to the internal sheath 110, and anexternal sheath 130 for enclosing the internal sheath 110 and thereinforcement members 120 together.

The internal sheath 110 has a multi-layered structure comprising a thinmetal film 111 a, a first insulation layer 111 b formed on a surface ofthe metal film 111 a, and a second insulation layer 111 c formed on theother surface of the metal film 111 a. The metal film 111 a may comprisebut is not limited to steel, stainless steel, and aluminum.

The first insulation layer 111 b acts as the outer surface of theinternal sheath 110 and may comprise but is not limited to nylon andpolyethylene terephthalate (PET).

The second insulation layer 111 c acts as the inner surface of theinternal sheath 110 and may comprise but is not limited to castpolypropylene (CPP).

The internal sheath 110 includes a rectangular first region 112 a thathas a predetermined area and a rectangular second region 112 b facingthe first region 112 a with a predetermined spacing between them thathas a larger area than the first region 112 a. The internal sheath 110also includes four third regions 112 c that are positioned on the edgesof the first regions 112 a and second regions 112 b to maintain anelectrode assembly 113 (described later) in place. An approximatelyplanar fourth region 112 d is positioned in front of one of the fourthird regions 112 c while further extending outward a predetermineddistance so that a protective circuit module 15 (described later) can beattached.

An electrode assembly 113 including a positive electrode plate 113 a, aseparator 113 b, and a negative electrode plate 113 c are placed in theinternal sheath 110, which is then sealed. The electrode assembly 113 iswound into a jelly roll to maximize surface area. Positive electrode tab114 a and negative electrode tab 114 b are coupled with the positiveelectrode plate 113 a and negative electrode plate 113 b, respectively,and extend a predetermined distance to the exterior of the internalsheath 110. In particular, the positive electrode tab 114 a and negativeelectrode tab 114 b extend to the exterior via the fourth region 112 dof the internal sheath 110.

A protective circuit module 115 is positioned in the fourth region 112 dof the internal sheath 110 to control charging/and discharging and toprevent overcharging. The positive electrode tab 114 a and the negativeelectrode tab 114 b are coupled with the protective circuit module 115while being coupled with the electrode assembly 113.

The reinforcement members 120 are fastened to the surfaces of theinternal sheath 110. In particular, the reinforcement members 120 arefastened to the first region 112 a and second region 112 b, which have acomparatively larger area than other regions of the internal sheath 110.The reinforcement members 120 may have the same area as the secondregion 112 b to increase the strength of the internal sheath 110 and tosuppress swelling. The reinforcement member 120 that is fastened to thefirst region 112 a is positioned above the protective circuit module 115with a predetermined spacing between them. The reinforcement members 120may have a smaller area than the second region 112 b, but the area ofthe reinforcement members 120 is not limited herein.

The reinforcement members 120 may comprise, but is not limited to ametal plate and a plastic plate. When the reinforcement members 120comprise a metal plate, the radiation performance further improves. Themetal may be steel, stainless steel, or aluminum, for example.

The reinforcement members 120 cover most of the surface of the internalsheath 110 to improve its strength and to prevent it from swellingoutward. When the reinforcement members 120 comprise a metal plate thathas excellent thermal conductivity, the radiation performance of theinternal sheath 110 improves.

The external sheath 130 is coupled with the outer surface of thereinforcement members 120 and to both third regions 112 c of theinternal sheath 110 that are positioned between the reinforcementmembers 120. The external sheath 130 may comprise a tube, a thermallycontractible tube, and a molded resin, for example.

The thermally contractible tube used as the external sheath 130 may be ahigh-molecular weight composite resin that is cross-linked byradioactive radiation and preferably contracts at a constant ratio ofabout 25-75% when heated at temperatures ranging from 90° C. to 130° C.A thermally contractible tube has excellent heat insulation propertiesand improves the electrical insulation, waterproofing, and exteriorprotection function of the internal sheath 110.

The resin is plasticized by heating plastic and shaping it with a moldto enclose the internal sheath 110 and the reinforcement members 120.The resin generally has a melting point ranging from 160° C. to 300° C.Preferably, the resin has a low melting point because extremely hightemperatures affect various electronic components 116 of the protectivecircuit module 115.

The external sheath 130 may have a structure wherein a side is open toexpose the protective circuit module 115 that is positioned in thefourth region 112 d of the internal sheath 110 to the exterior. A sideof the external sheath 130 that is opposite the protective circuitmodule 115 may also be open. Such a structure is naturally formed whenthe external sheath 130 is made of a tube or a thermally contractibletube. When the external sheath 130 comprises a resin, however, a sidethereof facing the protective circuit module 115, as well as theopposite side, may be enclosed. The external sheath 130 may also beinjection-molded to have a side open toward the protective circuitmodule 115, as well as a side open in the opposite direction, as when athermally contractible tube is used.

The outer sheath 130 provides insulation and prevents the metal film 111a of the internal sheath 110 from being exposed to the exterior.Therefore, the possibility that the metal film 111 a will beshort-circuited to a conducting external object decreases. In addition,the external sheath 130 protects the lithium polymer battery 110 of thepresent invention from its external environment.

FIG. 3 is a flowchart illustrating a method for manufacturing a lithiumpolymer battery according to an exemplary embodiment of the presentinvention. FIG. 4A, FIG. 4B, FIG. 4C, FIG. 4D, FIG. 4E, FIG. 4F, FIG.4G, and FIG. 4H are perspective views of the manufacturing steps thatare illustrated in FIG. 3. For convenience of understanding, FIG. 3 andFIG. 4A, FIG. 4B, FIG. 4C, FIG. 4D, FIG. 4E, FIG. 4F, FIG. 4G, and FIG.4H will now be referenced together to describe a method formanufacturing a lithium polymer battery according to the presentinvention.

As shown in FIG. 3, a method for manufacturing a lithium polymer battery100 according to an exemplary embodiment of the present inventionincludes the steps of S1 providing an internal sheath 110, S2 sealing anelectrode assembly 113, S3 connecting a protective circuit module 115,S4 fastening reinforcement members 120, and S5 forming an externalsheath 130.

In the step S1 of providing an internal sheath 110, a pouch-typeinternal sheath 110 is provided. As shown in FIG. 4A, the internalsheath 110 includes a first region 112 a that is formed at apredetermined depth in the interior of the internal sheath 110, a secondregion 112 b for covering the first region 112 a, a third region 112 cformed between the first and second regions 112 a and 112 b that is tobe bent in a predetermined direction at a later time, and a fourthregion 112 d on which a protective circuit module is to be placed at alater time. The layered structure of the internal sheath 110, asmentioned above, includes an approximately planar metal film 111 a, afirst insulation layer 111 b that is formed on a surface of the metalfilm 111 a, and a second insulation layer 111 c that is formed on theother surface of the metal film 111 a.

In the step S2 of sealing an electrode assembly 113, an electrodeassembly 113 is placed in the first region 112 a of the internal sheath110 which has been formed at a predetermined depth, as shown in FIG. 4B.The third region 112 c and fourth region 112 d of the internal sheath110 are then thermally bonded to maintain the electrode assembly 113 inplace.

The electrode assembly 113 has a positive electrode tab 114 a andnegative electrode tab 114 b that are formed thereon which extend apredetermined distance over the fourth region 112 d to the exterior, asshown in FIG. 4C. The third regions 112 c are bent toward the outersurface of the first region 112 a to minimize the volume of the internalsheath 110.

In the step S3 of connecting a protective circuit module 115, aprotective circuit module 115 is connected to the positive electrode tab114 a and negative electrode tab 114 b which extend a predetermineddistance through the internal sheath 110 to the exterior, as shown inFIG. 4D. A PTC device 116 may be interposed between the negativeelectrode tab 114 b and the protective circuit module 115 to interruptcurrent when the battery temperature rises above a reference level. ThePTC device 116 may also be positioned inside the protective circuitmodule 115. After the connecting step, the positive electrode tab 114 aand negative electrode tab 114 b are bent at a predetermined angle asshown in FIG. 4E and FIG. 4F to safely position the protective circuitmodule 115 in the fourth region 112 d of the internal sheath 110.

In the step S4 of fastening reinforcement members 120, reinforcementmembers 120 are fastened to the first region 112 a and second region 112b of the internal sheath 110, to respectively, as shown in FIG. 4G.Although the reinforcement members 120 are shown to have the same areaas the second region 112 b in the drawing, they may have the same areaas the first region 112 a or a smaller area than the first region 112 aand second region 112 b.

In the step S5 of forming an external sheath 130, an external sheath 130is formed to enclose the-reinforcement members 120 and the third region112 c of the internal sheath 110 as shown in FIG. 4H.

The external sheath 130 may generally be formed in two methods.

In the first method, the internal sheath 110 and reinforcement membersare inserted into a thermally contractible tube with the reinforcementmembers 120 fastened thereto. The thermally contractible tube is thenheated to a temperature of 90° C.-130° C. so that it contracts andcouples with the surface of the reinforcement members 120 and theinternal sheath 110. The protective circuit module 115 that is attachedto the internal sheath 110 and the opposite side of the internal sheath110, are exposed to the exterior. This allows the external sheath 130 ofthe lithium polymer battery 100 to have improved strength and to beformed simply and inexpensively. Alternatively, the external sheath 130may be formed by inserting the internal sheath 110 with thereinforcement members 120 fastened thereto into a conventional tube,instead of a thermally contractible tube.

In the second method, the internal sheath 110 may be positioned in amold with the reinforcement members 120 fastened thereto. A melted resinat a high temperature and pressure is then injected into the mold andcured so that it encloses the surface of the reinforcement members 120and the internal sheath 110. In this case, both the protective circuitmodule 115 and the opposite side of the internal sheath 110 may beenclosed by the melted resin, but this feature is not limited in thepresent invention.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A battery, comprising: an internal sheath with an electrode assemblypositioned therein; a reinforcement member that is coupled with an outersurface of the internal sheath; and an external sheath that integrallyencloses the internal sheath and the reinforcement member, wherein afirst side of the external sheath is open to an exterior so as to exposethe internal sheath, and wherein the external sheath comprises a tubecomprising the first side and a second side, the first side and thesecond side being open ends of the tube.
 2. The battery of claim 1,wherein the reinforcement member is a metal plate or a plastic plate. 3.The battery of claim 1, wherein the reinforcement member may comprise amaterial selected from the group consisting of steel, stainless steel,and aluminum.
 4. The battery of claim 1, wherein the external sheath isa thermally contractible tube.
 5. The battery of claim 1, furthercomprising a protective circuit module that is coupled with the internalsheath.
 6. The battery of claim 1, wherein the internal sheathcomprises: a rectangular first region with a predetermined area; arectangular second region that is spaced at a predetermined distancefrom the first region and has an area larger than that of the firstregion; and four third regions that are formed between the first regionand second region.
 7. The battery of claim 6, wherein the reinforcementmember comprises a first reinforcement member and a second reinforcementmember, wherein the first reinforcement member is coupled with the firstregion and the second reinforcement member is coupled with the secondregion of the internal sheath.
 8. The battery of claim 7, wherein thesecond reinforcement member has the same area as the second region. 9.The battery of claim 6, wherein the external sheath is coupled withouter surfaces of the reinforcement member and to two third regions ofthe internal sheath.
 10. A battery, comprising: an internal sheath withan electrode assembly positioned therein; a reinforcement member that iscoupled with an outer surface of the internal sheath; and an externalsheath that integrally encloses the internal sheath and thereinforcement member, wherein a first side of the external sheath isopen to an exterior so as to expose the internal sheath, wherein theinternal sheath comprises: a rectangular first region with apredetermined area; a rectangular second region that is spaced at apredetermined distance from the first region and has an area larger thanthat of the first region; and four third regions that are formed betweenthe first region and second region, wherein a second side opposite thefirst side of the external sheath is open to expose the third region ofthe internal sheath to the exterior.
 11. The battery of claim 1, whereinthe internal sheath comprises: a metal film; a first insulation layerdisposed on a first surface of the metal film; and a second insulationlayer disposed on a second surface of the metal film, the first surfaceand the second surface being opposite surfaces of the metal film. 12.The battery of claim 11, wherein the metal film comprises a materialselected from the group consisting of steel, stainless steel, andaluminum.
 13. The battery of claim 11, wherein the first insulationlayer comprises a material selected from the group consisting of nylonand polyethylene terephthalate (PET).
 14. The battery of claim 11,wherein the second insulation layer comprises cast polypropylene (CPP).15. The battery of claim 6, wherein the internal sheath furthercomprises a fourth region positioned in front of one of the four thirdregions and extending in a direction of the second region, wherein thefourth region is coupled to a protective circuit module, and wherein thefirst side of the external sheath is open to expose the fourth region ofthe internal sheath to the exterior.
 16. The battery of claim 11,wherein the external sheath comprises: two rectangular first regionsspaced apart from and facing each other; two rectangular second regionsspaced apart from and facing each other, wherein each of the secondregions is arranged between the two first regions, and wherein the firstside and the second side of the external sheath are each arrangedbetween the two second regions of the external sheath.
 17. The batteryof claim 1, wherein the internal sheath comprises a metal film disposedbetween a first insulation layer and a second insulation layer, andwherein the reinforcement member comprises a first metal plate and asecond metal plate spaced apart from the first metal plate, and theinternal sheath is disposed between the first metal plate and the secondmetal plate.
 18. A battery, comprising: an internal sheath with anelectrode assembly positioned therein; a reinforcement member that iscoupled with an outer surface of the internal sheath; and an externalsheath that integrally encloses the internal sheath and thereinforcement member, wherein a first side of the external sheath isopen to an exterior so as to expose the internal sheath, and wherein theexternal sheath comprises a molded resin comprising the first side and asecond side, the first side and the second side being open ends of themolded resin.